Need a support for existing VPC functionality

[digvijay-ukirde]

Description

Customers usually have an existing VPC and expect the solution (VSIs) to be deployed in the same.
Requirements:

1. Existing VPC: If the customer provides a VPC name, we should not create VPC and address prefix (default=null); and use the VPC to deploy the resources (subnet, VSI, SG etc)
2. Existing Subnet: If customer provide a subnet name, we should skip Subnet creation (default=null) and use the subnet to deploy the resources (VSI, SG, Gateway etc)
3. Existing Gateway: If customer provide a VPC where gateway already exists for a particular zone then use it and skip creating gateway

New or affected modules

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[vburckhardt]

• On VPC: current thinking is to see whether we could enhance landing zone module to skip vpc creation, in other word empty array in vpcs field.

  • scenario of existing vpc - enable creation of subnets / skip creation of subnets

• Expose the vsi secondary interface inputs in the landing zone module https://github.com/terraform-ibm-modules/terraform-ibm-landing-zone/blob/02648ac36c2eb15d9bceb8c43f200c6418a38735/variables.tf#L270

[Aayush-Abhyarthi]

Currently looking for ways to skip the vpc creation in the module so that the passed vpc can be used .

[ocofaigh]

This support was added in https://github.com/terraform-ibm-modules/terraform-ibm-landing-zone-vpc/releases/tag/v7.12.0
We are now looking to see if we can add support to the SLZ solution. Tracked at terraform-ibm-modules/terraform-ibm-landing-zone#635